1. Field
Apparatuses and methods consistent with exemplary embodiments relate to an impeller assembly of a fluid rotary machine and a method of manufacturing the same, and more particularly, to an impeller assembly that is easy to manufacture and that has a stable structure and a method of manufacturing the same.
2. Description of the Related Art
Compressors or pumps used for compressing a fluid include an impeller as a rotary machine structure. The impeller is configured to deliver rotary motion energy to a fluid by increasing the pressure of the fluid. The impeller includes a plurality of blades that guide movement of the fluid and deliver energy to the fluid. A shroud disposed to cover the impeller forms a moving path of the fluid together with the plurality of blades.
As known in the related art, the shorter the distance between the plurality of blades and the shroud, the higher the efficiency of a compressor. Thus, there is a recent trend that an impeller and a shroud are joined to form an integral structure, thereby maximizing the efficiency of a compressor.
In a technique of manufacturing an impeller assembly by joining an impeller and a shroud, a process of fixedly joining the plurality of blades of the impeller and the shroud should be performed. To this end, a process such as a casting process, a brazing process, electronic-beam welding, etc. is used.
For example, Japanese Laid-open Patent Publication No. 2004-353608 discloses a technique of reinforcing joining of a shroud to an impeller by welding a shroud to the impeller, in which the impeller and the shroud are fixed to each other by contacting and welding the impeller and the shroud together.
However, if an impeller assembly is manufactured according to this method, it is difficult to manufacture the impeller assembly when the overall size of the impeller assembly increases. That is, when the overall size of the impeller assembly increases, the size and thickness of the shroud naturally also increase. In this case, however, input welding power is excessively generated to weld the thick shroud and the impeller together and thus the impeller and the shroud may excessively deform.
Although use of a thin shroud may be considered to minimize deformation in the welding process, the shroud cannot stably support blades of an impeller assembly when the shroud is designed to be thin, and the structural stability and the performance of the fluid machine may be deteriorated.
In the related art, an impeller assembly may also be manufactured using a casting process but different contraction characteristics due to different masses of portions thereof arise when a melted metal is hardened. In particular, a fillet portion of the impeller assembly excessively deforms, thereby preventing the outlines of three-dimensional (3D) blades from being precisely formed.
Alternatively, in the related art, an impeller assembly may be manufactured using a vacuum brazing process of uniting a base material and a filler material having a low melting point by melting the filler material without causing damage to the base material. However, in the vacuum brazing process, when a resultant structure is heated to a range of reaction temperatures and is then cooled, cooling rates of portions of the resultant structure are different due to a variation in the thickness thereof, thereby causing a fillet portion to deform to a great extent. Therefore, the impeller assembly cannot be used when the deformation is not in an allowable design range and cannot be applied to products used at high rotations per minute (RPM) since an adhesive strength of portions united using the brazing process is lower than that of portions united using the welding process.
When an impeller and a shroud are joined together by using both the welding process and the brazing process, a fillet portion at which the shroud and the impeller are united to each other may be manufactured using a brazing filler. In the related art, since the fillet portion is formed in a small size having a radius of about 0.8 mm, stress is intensively applied to the fillet portion. Accordingly, it is difficult to apply impeller assemblies manufactured using the methods described above to large-sized products.
Furthermore, a closed type impeller assembly may be manufactured by machining such as cutting, drilling, etc. However, when the overall size of an impeller assembly is small or the heights of blades are low, it is difficult to secure a working space into which processing equipment can be positioned.